GHCN: High Alt, High Lat, Rural
In the Summary for Policy Makers in Watts’ and D’Aleo’s Surface Temperature Records: Policy Driven Deception, there is the following claim:
5. There has been a severe bias towards removing higher-altitude, higher-latitude, and rural stations, leading to a further serious overstatement of warming.
Here I examine the effect of removing high altitude, high latitude, and rural stations using the GHCN raw data and applying the published CRU station gridding and averaging code.
First: How does losing high altitude stations affect the temperature anomaly plot?
I use 3188 GHCN raw stations for the baseline series. Then I remove all the stations over 1000m. (Very roughly 10% of them). The first plot is the baseline (red) and the low altitude series (blue), The second plot is the difference between the two series (same scale on both plots).
Second: How does losing high latitude stations affect the temperature anomaly plot?
Again, I use the 3188 GHCN raw baseline. Then I remove all stations above 60N and below 60S. The baseline and low latitude stations are then compared.
Third: How does the urban stations affect the trend?
Here I used the
GRUMP* GPW gridded population data at 2.5′ resolution to find stations that are possibly urban. I applied a filter that removed all stations in areas with more than 100 persons per square mile. This is much lower than the US Census definition of an urban area (1000/sq mile) or urban cluster (UA + neighboring regions of 500/sq mile).
Of course, the full claim is that the decreasing number of HA, HL, and rural stations in recent decades has artificially inflated the global temperature anomaly in recent decades. Comparison of the satellite anomaly trend and satellite anomalies with the surface records (sea+land) is sufficient to falsify that claim – unless the satellite record has also been artificially manipulated to show the same anomalies
Update 2010 02 13: Conflated GRUMP with GPW. The later data set was used in this analysis.
Zeke Hausfather @ Yale Forum on Climate Change and the Media
Roy Spencer @ Global Warming
Tamino @ Open Mind